The present invention relates generally to the field of computer resource virtualization, and more particularly to logical partition mobility between physical computing systems.
Live partition mobility (LPM) allows a system administrator or other user to migrate a logical partition (LPAR), or virtual machine (VM), from one server computer (source server computer), or central electronics complex (CEC), to another CEC (destination server computer) without disrupting the services provided by the LPAR. The LPAR that is being moved in the LPM operation is known as the “mobile partition.” The mobile partition accesses necessary storage devices divided into logical units, and identified by logical unit numbers (LUNs) using virtual ports which correspond to physical ports on the host CEC that are connected to a storage area network (SAN). A common requirement for LPM is that the LUN(s) that the mobile partition accesses must be configured for access by both the source server computer and the destination server computer. The source server computer and the destination server computer have access to the same network and SAN(s). Generally, the mobile partition is fully virtualized, which means that the mobile partition has no dedicated physical I/O adapters associated with the mobile partition.
Each virtual connection between the mobile partition and the SAN has two world wide names (WWNs), or world wide port names (WWPNs). One of the WWPNs is a primary WWPN and the other is a secondary WWPN. The mobile partition uses the WWPNs to access one or more LUNs via the SAN. Traditionally, the mobile partition places a reservation on one or more LUNs that it accesses via the SAN. In traditional SAN architectures, reservations are exclusive, which means that one and only one LPAR can reserve a LUN at any point in time. More recently, shared reservations have developed, such as SCSI-3, in which one or more LPARs can access a LUN, with varying priorities and privileges, depending on the specific LPAR.
During traditional LPM operations, a controlling computer, such as a hardware management console (HMC) verifies that the destination server computer has sufficient resources available to support the mobile partition. Once the verification is complete, the HMC copies the mobile partition from the source server computer to the destination server computer. After the copy occurs, the mobile partition copy still existing on the source server computer is using the primary WWPN to access one or more LUNs via the SAN, and holds an exclusive reservation on the LUN(s). The mobile partition copy on the destination server computer uses the alternate WWPN to access the one or more LUNs required by the mobile partition. In order for the mobile partition copy on the destination server computer to establish a reservation on the required LUN(s), the mobile partition copy on the source server computer releases the exclusive reservation held on the LUN(s). Sometime after the mobile partition copy on the source server computer releases the reservation, the mobile partition copy on the destination server computer establishes an exclusive reservation on the required LUN(s) using the alternate WWPN.